1. Field of the Invention
The present invention relates to a thin film transistor (TFT), a method for fabricating the TFT, and an organic light emitting display device (OLED) constructed with the TFT, and more particularly, to a TFT which is fabricated using Joule's heat to improve its characteristics, a method for fabricating the TFT, and an OLED constructed with the TFT.
2. Description of the Related Art
In recent years, much attention has been paid to flat panel display devices (FPDs) that can overcome the problems faced by contemporary heavy and large-sized display devices such as a cathode ray tube (CRT) display. The FPDs may be a liquid crystal display device (LCD), an organic light emitting display device (OLED) or a plasma display panel (PDP).
The FPDs are typically constructed with a thin film transistor (TFT), which is required to operate at high speed in response to a given signal and is required to exhibit uniform characteristics over the entire substrate of the TFT. In order to satisfy these requirements, it is most important to control the characteristics of a semiconductor layer of the TFT.
The semiconductor layer is typically constructed by crystallizing amorphous silicon (a-Si) into a polycrystalline silicon (poly-Si) layer. The crystallization of the semiconductor layer may be performed using a solid phase crystallization (SPC) process, an excimer laser annealing (ELA) process, a metal induced crystallization (MIC) process or a metal induced lateral crystallization (MILC) process. Specifically, the SPC process includes a step of annealing an a-Si layer for several to several tens of hours at temperatures below 700° C. where a glass substrate used in the TFT may be undesirably deformed. The ELA process includes a step of partially heating an a-Si layer to reach a high temperature in a short time by irradiating excimer lasers on the a-Si layer. The MIC process includes a step of bringing a metal such as nickel (Ni), palladium (Pd), gold (Au) or aluminum (Al) into contact with an a-Si layer, or a step of injecting the metal into the a-Si layer to induce a phase change of the a-Si layer into a poly-Si layer. The MILC process includes a step of sequentially inducing the crystallization of an a-Si layer while laterally diffusing silicide obtained by a reaction between a metal and silicon.
Since the SPC process involves annealing a substrate at a high temperature for a long period of time, the substrate may be seriously damaged. Also, the ELA process requires expensive laser apparatuses and a high maintenance fee. Further, both the MIC and MILC processes consume too much time in order to crystallize an a-Si layer into a poly-Si layer.